Many networks such as local and wide area networks (LAN/WAN) structures are used to carry and distribute data communication signals between devices. Various network elements include hubs, switches, routers, and bridges, peripheral devices, such as, but not limited to, printers, data servers, desktop personal computers (PCs), portable PCs and personal data assistants (PDAs) equipped with network interface cards. Devices that connect to the network structure use power to enable operation. Power of the devices may be supplied by either an internal or an external power supply such as batteries or an AC power via a connection to an electrical outlet.
Some network solutions can distribute power over the network in combination with data communications. Power distribution over a network consolidates power and data communications over a single network connection to reduce installation costs, ensures power to network elements in the event of a traditional power failure, and enables reduction in the number of power cables, AC to DC adapters, and/or AC power supplies which may create fire and physical hazards. Additionally, power distributed over a network such as an Ethernet network may function as an uninterruptible power supply (UPS) to components or devices that normally would be powered using a dedicated UPS.
Additionally, network appliances, for example voice-over-Internet-Protocol (VOIP) telephones and other devices, are increasingly deployed and consume power. When compared to traditional counterparts, network appliances use an additional power feed. One drawback of VOIP telephony is that in the event of a power failure the ability to contact emergency services via an independently powered telephone is removed. The ability to distribute power to network appliances or circuits enable network appliances such as a VOIP telephone to operate in a fashion similar to ordinary analog telephone networks currently in use.
Distribution of power over Ethernet (PoE) network connections is in part governed by the Institute of Electrical and Electronics Engineers (IEEE) Standard 802.3 and other relevant standards, standards that are incorporated herein by reference. However, power distribution schemes within a network environment typically employ cumbersome, real estate intensive, magnetic transformers. Additionally, power over Ethernet (PoE) specifications under the IEEE 802.3 standard are stringent and often limit allowable power.
Silicon-based electronic devices are susceptible to damage from spurious events that exert voltage/current stresses exceeding the normal operating limits of the devices. Electrostatic discharge (ESD) is sudden, brief electric current that flows between objects at different electrical potentials, typically momentary unwanted and potentially destructive currents that may cause damage to electronic equipment. ESD typically arises as air discharge and cable discharge, which is particularly insidious. ESD is common problem that is difficult to address. Stress events can be surges on the power line originating from causes such as lightning strikes, but can also originate from human body discharge. If the stress event lasts sufficiently long or the spike in voltage is sufficiently severe, momentary current along a temporary path through the substrate can cause failure through overheating, which causes the silicon or metal to reach the melting point. Lighting and electro-static discharge (ESD) events can be very fast, with time constants as short as 6 ns. The maximum voltage overstress during an event is typically determined by the reaction time of protection devices so that small parasitic changes can cause large variations in the magnitude of overstress.